There are many types of light fixtures. Light fixtures may utilize incandescent lamps, fluorescent lamps, metal halide lamps, and others. One of the most widely used light fixtures for large buildings, stores, warehouses, manufacturing facilities, and the like is the fluorescent light fixture. Fluorescent light fixtures are efficient to operate and are capable of illuminating relatively large areas.
A typical fluorescent light fixture has an elongated housing, usually made of metal or plastic with a downwardly opening elongated cavity in which is carried one or more tubular fluorescent lamps for emitting light below the fixture. The central element in a fluorescent lamp is a sealed glass tube. The tube contains a small amount of mercury and an inert gas, typically argon, kept under very low pressure. The tube also contains a phosphor powder. The phosphor powder is coated along the inside of the glass tube. The tube has two electrodes, one at each end, which are wired to an electrical circuit. The electrical circuit is connected to an alternating current (AC) source. When a fluorescent lamp is turned on, the current flows through the electrical circuit to the electrodes. The current stimulates the mercury atoms, causing them to release ultraviolet photons. These photons in turn stimulate the phosphor, which emits visible light photons.
In most commercial buildings, it is not necessary to keep all of the light fixtures illuminated after normal business hours. Indeed, it is generally desirable to keep after-hours lighting to the minimum necessary for maintenance and security personnel to be able to effectively perform their duties. Presently, this is accomplished by turning on only a few of the available light fixtures.
Emergency lighting is utilized in most buildings to provide light for egress and to direct occupants toward the exits in case of a loss of main power to a building. This is generally accomplished by installing exit and emergency lighting fixtures at various locations, such as corridors, stairwells, ramps, escalators, aisles, exit passageways, and the like. The exit and emergency lighting fixtures are generally self-contained and may utilize small batteries which are kept charged in case of main power failure.
In some situations, it is desirable to have only a minimal amount of light within a room. For example, when a person is giving a presentation that includes the display of pictures and/or video, it is typically desirable for the room to be somewhat dim but not completely dark. As another example, some individuals like to reduce the amount of light within their office when they are working on a computer, in order to maximize the contrast between their computer monitor and the surrounding area. There are numerous other examples of situations where it may be desirable for the light fixtures in a particular area to be able to satisfy low light requirements, i.e., to provide only a minimal amount of light.
In view of the foregoing, benefits may be realized by improved light fixtures that are capable of satisfying after-hours lighting requirements more efficiently and conveniently than presently known light fixtures. Additional benefits may be realized if such improved light fixtures were also capable of providing emergency lighting in situations where power to a building has been lost. Yet additional benefits may be realized if such improved light fixtures were also capable of satisfying low light requirements.